1. Field of Invention
The invention relates to an ink-jet head for printing by ejecting ink onto an image recording medium, and to an ink-jet printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink supplied from an ink tank to pressure chambers. The ink-jet head selectively applies pressure to each pressure chamber to eject ink through a nozzle. As a means for selectively applying pressure to the pressure chambers, an actuator unit having ceramic laminated piezoelectric sheets may be used.
As an example, a generally-known ink-jet head has one actuator unit in which continuous flat piezoelectric sheets extending over a plurality of pressure chambers are laminated. At least one of the piezoelectric sheets is sandwiched by a common electrode common to the pressure chambers and is kept at the ground potential. The actuator unit also includes and many individual electrodes, i.e., driving electrodes, disposed at positions corresponding to the respective pressure chambers. When an individual electrode on one face of the sheet is set at a different potential from the potential of the common electrode on the other face, the part of piezoelectric sheet being sandwiched by the individual and common electrodes, and which is polarized in its thickness, is expanded or contracted in its thickness direction, by the so-called longitudinal piezoelectric effect. In this case, the parts of the piezoelectric sheet sandwiched by the driving and common electrodes work as active layers(active portions) that are deformed by the piezoelectric effect when an external electric field is applied to them. The volumes of the corresponding pressure chambers thereby change, so ink can be ejected toward an image recording medium through nozzles communicating with the respective pressure chambers.
Recently, in an ink-jet head such as that described above, as the pressure chambers are disposed at a higher density in order to meet demands of increasing the image resolution and increasing the printing speed, a problem of crosstalk occurs. That is, when the active layer corresponding to a pressure chamber deforms, a portion of the piezoelectric sheet corresponding to another pressure chamber neighboring that pressure chamber can deform accordingly. As a result, ink is ejected through an ink ejection port that should not be used for ink ejection in this case, and the ink ejection amount may be more or less than the desired amount. When such crosstalk occurs, the quality of an image recording medium image may deteriorate. Therefore, to improve the quality of such an ink-jet printer, suppression of crosstalk is important.